I'm not saying we shouldn't have cosmologies. I'm saying that each setting should have a distinct cosmology that makes sense for that setting. When Dragonlance came out, there was very little detail about the cosmology. You basically had Krynn, some sort of very undefined heaven and the abyss. That was it. There was no Hell at all in Dragonlance. Which makes sense. If Takhisis is the big, evil goddess of everything evil, it doesn't make a whole lot of sense to have Asmodeus sitting over there twirling his mustache. And, since planar travel isn't really a thing in DL, you don't need this extensive cosmology either. Where do Elementals come from if the PC casts Summon Elemental? Who cares? It comes from somewhere else. I don't need the Princes of Elemental Evil in Dragonlance.
Primeval Thule, which is the setting I'm using now, doesn't have a cosmology at all, really. Extraplanar creatures aren't actually extraplanar, they're what is termed Extraterrene. IOW, they're from other planets. Other realities might exist, but, again, it's outside the scope of the setting really, so, it's completely undefined. PT has a pretty strong "science fantasy" vibe, so, it makes sense that you don't have these extensive planar set-ups.
I'm actualy pretty disappointed with MToF, because they simply went with the lowest common denominator. Warmed over Planescape which is the same thing we've been getting for the past thirty years. Whoopee. In a way, I should be thankful I suppose. It does mean that yet again, I have zero interest in the planar stuff that WotC (or TSR) bangs out and it saves me the thirty bucks or so.